The 3rd-Generation Partnership Project (3GPP) has developed specifications for a high-speed wireless packet data link based on Code-Division Multiple Access (CDMA) technology. Specifications for this so-called High-Speed Packet Access (HSPA) technology include support for both a high-speed downlink (High-Speed Downlink Packet Access, or HSDPA) and a high-speed uplink (known as Enhanced Uplink, EUL, or High-Speed Uplink Packet Access, HSUPA).
In the HSPA uplink as currently specified, data-to-control interference is a significant limitation. As one tries to increase data rates, the interference from the packet data channel (E-DCH) to control channels, e.g., DPCCH, RACH, etc. becomes significant. To permit reliable Random Access Channel (RACH) detection and to ensure adequate coverage, the rise-over-thermal (RoT) of the high-speed uplink must be maintained at a relatively low level. In addition, stability concerns for high data rates also require that RoT be maintained at low levels. The end result is that high uplink data rates are difficult to achieve in practice, since achieving high data rates requires that RoT be allowed to reach relatively high levels.
One way of to increase the uplink data rates available to a mobile station is to permit dual-carrier operation in the uplink. This is supported in Release 9 of 3GPP's HSPA standards. With this approach, the two HSPA carriers used by a mobile station can be configured so that the primary carrier carries all legacy traffic and the majority of control channels, thus allowing the supplementary carrier to carry only data-related channels. (Techniques for configuring HSPA carriers in this manner are described in U.S. patent application Ser. No. 12/614,526, filed Nov. 9, 2009, the entire contents of which are incorporated herein by reference.) However, while this allows higher RoT levels on the supplementary carrier, and thus a higher overall uplink data rate, performance is still limited, since it is difficult to eliminate all control channels from the supplementary carrier.